The present invention relates to the general field of the electrical cables used in the transmission of electrical power at high voltage and to the limitation of the appearance of partial discharges within these cables. The invention more particularly but not exclusively relates to the limitation of the appearance of partial discharges in the electrical harnesses and cables used in aircraft.
The advent of increasingly electrical airplanes has resulted in the increased use of pieces of electrical equipment that must be supplied with power and controlled, in environments that are sometimes hostile, by virtue of many electrical harnesses. An electrical harness is an assembly of electrical cables or wires of different gauges grouped into an electrical bundle, the cables or wires being run together and ending in connectors. In certain cases the harness may be shielded or placed in metal wireways in order to protect them from electromagnetic effects. Its reliability is indispensable for the availability of all of the devices of the electrical power system. The presence of insulators makes it possible to ensure the isolation of the various electric circuits when the cables are assembled into a harness. Considered together, all the solid and gaseous insulators that insulate the cables from each other and the conductive structures located in proximity to the harness are called the electrical insulation system (EIS).
The use of these pieces of electrical equipment induces the appearance of undesirable effects, in particular when the pieces of equipment are subjected to high electrical voltages (for example AC voltages of 230 VAC, DC voltages of +/−270 VDC, or even 540 VDC). These high voltages, associated with aeronautical environments in which pressure, temperature and moisture level may notably vary depending on the flight phases of the aircraft, lead to the appearance of partial discharges in the electrical insulation system of the cables of the harness.
Partial discharges are localized electrical discharges that may partially short-circuit the insulating interval separating two conductors of a harness. In practice, they manifest themselves in the form of electric micro-arcs in the gases located in proximity to (for example between two insulated cables) or in the interior of the insulator (for example in cavities) of the electrical cables. These discharges can lead to the slow and gradual degradation of the insulator of the electrical insulation system of the cables, and cause its premature rupture. The reliability and the availability of the electrical power chain may therefore be greatly impacted by these partial discharges.
The high voltages used increase the electric field in the gases of the EIS, thereby leading to the appearance of partial discharges. One known solution to this problem consists in increasing the distance between neighboring cables, this having the effect of decreasing this electric field. Another solution is to differently distribute the electric field between the insulator and the gases of the EIS, for example using cables having an insulating jacket of much larger thickness. Increasing this thickness allows the electric field in the insulating part of the EIS to be increased and the electric field in the gas between the cables to be decreased, this decreasing the appearance of partial discharges.
However, such a solution poses an integration problem because the weight of the harness and its general bulk are considerably increased. But the current tendency is on the contrary to decrease the weight and bulk of elements present in aircraft in order in particular to decrease its fuel consumption.
It would therefore be desirable to have at one's disposal compact and light harnesses and electrical cables that would make it possible to prevent the appearance of partial discharges.